Method of making cast iron



Patented July 6, 1937 PATENT OFFICE 2,086,098 METHOD or MAKING CAST moN Oliver. Smalley, Pittsburgh, Pa., a'ssignor to Meehanite Metal Corporation, Pittsburgh, Pa., a corporation of Tennessee No Drawing. Application June 8, 1935, Serial No. 25,668

Claims.

This invention relates to the treatment of molten metal in the manufacture of castings and has as an object the production of superior gray iron castings of improved tensile and transverse 5 strength, as well as greater density and hardness.

Heretofore, it has been the practice in the manufacture of gray iron castings to add to the molten metal a suitable agent, in order to obtain the carbon in the desired forms. For example, in .the breaking down of iron carbide in the metal during solidification, a silicide substantially free from iron has been added to molten white iron, and gray iron thus produced in accordance with the patent to Meehan 1,498,068, June 24, 1924. Also a later patent to Meehan No. 1,683,086 de-' scribes a process for improving molten ironwhich, when cast, ordinarily would be gray in character, by introducing into the molten metal a silicide which is substantially free from iron, such as cal- 20 cium silicide, together with a second graph-itizing agent, i. e. an intensifying agent, such as, nickel, aluminum, titanium, vanadian or a second alkaline earth metal. These metals, however, do not increase the strength, hardness and toughness 5 of the iron at the same time that they intensify the graphite content, and are employed by Meehan in such small quantities as to be practically negligible insofar as the advantageous effects obtained by the present invention are con- 30 cerned.

I have discovered that the amount of graphitic carbon in any molten iron madefrom a steel rich mix which, when cast, will be gray in character is increased by the addition of a small quantity 35 of copper (Mendeleefs periodic table, group 1, series 4) and simultaneously the density, strength and hardnes: of the final casting is appreciably enhanced. These results are achieved whether or not a graphitizing agent such as mentioned in 40 the Meehan patents is used. In other words, the copper of itself constitutes the graphitizing agent, or acts as an intensifier in conjunction with another graphitizing agent.

By gray iron, as applied to molten iron, I mean such molten iron as will produce castings in which more or less graphitic carbon is present.

In order that the invention may be understood by those skilled in the art, the following examples illustrate the eiIect of adding varying quantities of copper up to 3% to cast iron mixes, where-the mix contains steel in quantities of 70% or more and calcium silicide in the amount of 70 ounces per ton:

6 Tensile Transverse Percent 35 23 23}; strength strength Defleet copper chm o in lbs. per 18" center sq. in. 1.2" bar above to a steel rich mix containing 70% steel, 5

this is simply exemplary since the invention is equally operable when a steel rich mix hasa content of as low as substantially 25% steel and a carbon content up to substantially 3.2%.

The normal reaction of a graphitizer is to soften a casting and reduce its density. For example, a decrease in the chilling quality of iron from 22/32 to 15/32, which takes place when copper in amounts up to 2% is added, (see above table) would normally be accompanied by a drop in Brinell hardness from 229 to 197, but when copper is employed as the intensifying agent, the Brinell hardness actually increases from ,229 to 285. This is very unusual and decidedly unexpected, as 2% copper iron contains more graphite than ordinary gray iron, and should, therefore be softer and of less strength.

The-copper may be added in the cupola with the metal charge as elemental copper alloy. When a copper silicon alloy is employed, either the silicon or the copper may predominate, e. g., either an alloy containing 70% copper and 30% silicon, or one containing 30% copper and 70% silicon may be added. As an alternative method the copper may be introduced in the ladle as a copper calciumsilicide alloy containlng'the fol- As a further possibility copper shot or scrap in conjunction with a calcium, magnesium, or barium silicon alloy may be supplied to the stream of the molten iron as it runs into the ladle.

Among the various graphitizing agents in conjunction wlth which copper has been satisfactory in accordance with this invention are:-calcium, magnesium, barium, strontium, sodium, potassium, zirconium, titanium, beryllium, cerium, nickel, molybdenum, silicides of these metals, as well as silicon and ferro-silicon. Therefore, it is to be understood that reference to calcium sillcide herein is purely by way of example.

With respect to the percentage of copper employed, this, of course, will vary, as is likewise true when another graphltizing agent is employed, dependent upon the properties and characteristics of the iron being treated. For example, calcium silicide is added in amounts sufflcient to produce an appreciable graphitizing action, and the copper is employed in a quantity to promote and intensify the transformation of the combined carbon into graphite. In most cases, about three percent, more or less, of copper is employed.

The present invention, as will be understood,

relates to the production of gray iron castings produced from steel rich mixes and particularly to the use of copper for the purposes hereinbefore explained. It isrecognized that the addition of copper to improve the corrosion resistant properties of cast iron is well known, e. g., a usual expedient being to add .6 to .8 per cent of copper to ordinary cast iron for this purpose.

When 1 refer to cast iron as gray, I mean cast iron containing graphitic carbon in such absence quantities as to make it machinable when cast V insand. By mix", I mean the charge in either sufllcient to increase appreciably the strength properties, density and hardness of the iron.

2. That improvement in the art of making cast iron which comprises adding to a steel rich mix having a steel content of at least 25% and which will normally produce a gray iron casting, an

alkaline earth silicide and copper from approximately 1% to approximately 3% whereby to increase the strength properties, density and hardness of the iron.

3. The process of making gray iron castings which comprises melting a cast iron charge containing over steel and which would normally produce a gray iron casting and adding thereto copper from 1% to 3% and calcium silicide as a graphitizing agent.

4. As a new article of manufacture, a gray cast iron produced from a gray iron producing mix containing more than 25% steel and to which has been added copper in appreciable and essential amount from 1% to about 3%, said cast troducing copper from 1% to about 3% and a graphitizing agent into a steel rich cast iron mix containing more than 25% of steel and which would normally be gray when sand cast.

OLIVER. SMALLEY. 

